Panoramic photography often employs specialized cameras, equipment and/or software, to capture a sequence of images that are reconstructed into a single image that takes the form of a wide strip with an elongated field of view. Panoramic photography is sometimes known as wide format photography. Typically, a panoramic image shows a field of view that is greater than that of a film camera equipped with a wide angle lens. And a typical film camera equipped with a wide angle lens can generally capture an image with a field of view that covers about 90 degrees across the diagonal of the captured image, e.g., a 35 millimeter film camera with a 22 degree lens can capture such an image. One way to capture a panoramic image is to mount a film camera on a tripod and as the camera is physically rotated about its axis, a succession of images of a scene are taken that are subsequently stitched together by physically cutting and pasting together strips of exposed film where the boundaries between the edges of the film are carefully aligned. In some cases, a wider than usual strip of film can be used with a film camera that employs special movable or stereo optics. In other film cameras, conventional format film, such as 35 millimeter, can be masked during the exposure in the camera to provide a wide aspect or panoramic effect.
Recently, the benefits of electronic photography have led to the general acceptance of digital cameras, which, unlike their film-based counterparts, store captured images in a digital memory such as flash memory. And some digital cameras can also provide a “panorama” feature, which allows a user of the digital camera to capture a sequence of adjacent images that are subsequently “stitched” together into a single image with a wide coverage of field. For example, some digital cameras with a panoramic feature can interface with a personal computer that provides software to externally join together two or more images at their edge boundaries to generate a single image with a wide panoramic format for display on the personal computer.
Generally, when creating panoramic images, the exposure settings are preset according to the first image and kept constant, in order to avoid unpleasant lighting changes in the stitched panorama result.
Images captured by digital cameras are most commonly Low Dynamic Range (LDR) images, in which each image pixel comprises a limited number of digital bits per color. The number of digital bits per pixel is called the digital pixel bit width value. This number is commonly 8 bits. Such 8-bit pixels can be used to form an image with 256 different gray levels for each color at each pixel location. In a LDR image of a scene, shadow areas of the scene are depicted as being completely black (under exposed), bright sunlit areas of the scene are depicted as being completely white (over exposed), and scene areas in between are shown in a range of gray levels. A High Dynamic Range (HDR) image is one that has digital pixel bit width values of greater than 8 bits; 16 bits per pixel is a possible value. In such an image the full range of gray levels that appear in a physical scene can be displayed. These gray levels provide image details that are present in the scene's shadow regions, highlight regions and mid tone regions that are missing from the LDR image. Thus, in an HDR image, aside from the mid-illuminated areas of the scene, even scene details in dark areas (e.g., shadows) or well-lighted areas (sunlight) can be accurately represented.
An HDR image can be captured by acquiring multiple LDR images of a scene that are captured at different exposure levels. These multiple LDR images are called a bracketed exposed image series. A low exposure level will properly capture the gray levels in scene areas fully illuminated by bright sunlight and a high exposure level will properly capture the gray levels in scene areas that are dimly lighted (e.g., areas that are shadowed by other objects like buildings). However, at the low exposure level the areas of the scene in shadow will be completely dark and will show no detail, and the midtone areas will lose detail. Further, at the high exposure level, the highlights of the scene will be completely saturated, and will show no detail, and the mid-tone areas will again lose detail. Thus, a third, mid exposure level image, which properly captures mid level gray shades, may be used as well. By mixing these three LDR images, an HDR image can be generated that depicts the full gray scale range of the scene.